The solution, according to the designers of Beach Vault, is to bury them.
Beach Vault is cylindrical plastic container that let's you stash your stuff underground and out of sight. Large enough to store objects such as tablets and Kindles, Beach Vault is a sealable, watertight capsule that is screwed into the sand under the custom-made towel. A flap designed to hold a pillow conceals a hole that fits around the mouth of the capsule, intended to give easy access to your items.
A little discretion can do a lot for one's peace of mind at the beach, a classic hunting ground for petty thieves. It must be said, however, that a closed plastic container won't do much to stop such opportunists if they think they've scoped out an unguarded jackpot. If you're after a more high-tech security option, the motion-sensitive, combination locked Yelpie portable safe may be worth a look.
The company is currently raising funds on Kickstarter for the Beach Vault, where a pledge of US$35 will put you in line for one of the capsules and the accompanying towel. If enough funds are raised, it plans to begin shipping in August 2014.